DE102020214128B4 - Rules of an X-ray pulse chain generated by a linear accelerator system - Google Patents

Abstract

The invention relates to a method for controlling an X-ray pulse chain generated by means of a linear accelerator system with a first multi-amplitude X-ray pulse and a second multi-amplitude X-ray pulse, having the following steps:- modulating a first electron beam generated by means of an electron source of the linear accelerator system within a first high-frequency pulse duration, the first multi-amplitude x-ray pulse is generated during modulation of the first electron beam,- measuring time-resolved actual values of the first multi-amplitude x-ray pulse by means of a measuring unit,- adjusting at least one pulse parameter by means of a control unit depending on a comparison of the specified multi-amplitude x-ray pulse profile and the measured time-resolved Actual values, and- modulating a second electron beam generated by the electron source within a second high frequency quenzpulse duration as a function of the at least one adjusted pulse parameter for generating the second multi-amplitude X-ray pulse, whereby the X-ray pulse train is regulated.

Description

The invention relates to a method for controlling an X-ray pulse chain generated by means of a linear accelerator system with a first multi-amplitude X-ray pulse and a second multi-amplitude X-ray pulse, an associated linear accelerator system and an associated computer program product.

A linear accelerator system is known to be used to accelerate charged particles, particularly electrons generated by an electron source, along a straight line. Depending on the type of linear accelerator system, the electrons are accelerated to energy values above 1 MeV in a linear accelerator cavity, in particular by means of a high-frequency source. An energy value at a point in time typically correlates directly with a dose value at that point in time.

X-ray pulses with different energy values are advantageously used when x-raying goods in transit, for example during a customs or security check, in order to enable material discrimination and thus determination of different types of goods in transit. Ogorodnikov et al. discloses in "Processing of interlaced images in 4-10 MeV dual energy customs system for material recognition", Physical Review Special Topics - Accelerator and Beams, Volume 5, 104701 (2002) the use of different energy values for material discrimination.

• Beispielsweise offenbart WO 2015/175 751 A1 einen Röntgenstrahlenpuls mit mehreren Energiewerten. Ein solcher Puls kann grundsätzlich Mehrfachamplituden-Röntgenstrahlenpuls genannt werden. Je nach zeitlicher Verteilung und Betrag der Energiewerte kann der Röntgenstrahlenpuls zumindest zwei Intrapulse mit verschiedenen Energiewerten aufweisen, wobei die zumindest zwei Intrapulse zeitlich betrachtet innerhalb einer Hochfrequenzpulsdauer generiert werden. Die zumindest zwei Intrapulse bilden beispielsweise eine weitere Art an Mehrfachamplituden-Röntgenstrahlenpuls.

While in earlier linear accelerator systems only the energy values in successive radio frequency and X-ray pulses could be varied, it is now known that a single electron beam pulse or X-ray pulse can have different energy values:

• For example disclosed WO 2015/175 751 A1 an X-ray pulse with multiple energy levels. Such a pulse can basically be called a multi-amplitude X-ray pulse. Depending on the temporal distribution and amount of the energy values, the X-ray pulse can have at least two intra-pulses with different energy values, the at least two intra-pulses being generated within a radio-frequency pulse duration in terms of time. The at least two intrapulses form, for example, another type of multi-amplitude X-ray pulse.

From the US 2014/0 270 086 A1 control of the X-ray energy for an intrapulse is known. the U.S. 2012/0 093 289 A1 describes X-ray sources with varying spectrum and intensity for improved material discrimination. More linear accelerator systems are from the US 2018/0 270 941 A1 , US 2019/0 357 343 A1 and US 2016/0 050 741 A1 known.

the DE 10 2016 222 373 A1 describes a method for operating a linear accelerator, in which charged particles are emitted from a particle source and are accelerated in an acceleration device by means of a high-frequency alternating field in such a way that pulses of charged particles are generated. A particle stream emitted by the particle source is varied within an HF pulse duration of the high-frequency pulse in such a way that the pulse formed within the HF pulse duration has at least two partial pulses with different average energies per particle.

While a control of the linear accelerator system with successive radio frequency and X-ray pulses may take up to several milliseconds and typically only considers an integrated amplitude value of the previous pulse, a control of an X-ray pulse chain with a first multi-amplitude X-ray pulse and a second multi-amplitude X-ray pulse requires additional information. This is due in particular to the fact that a transient response and/or a drift property of the linear accelerator system within the radio-frequency pulse duration should be taken into account when generating the multi-amplitude X-ray pulse.

The invention is based on the object of specifying a method for regulating an X-ray pulse chain generated by means of a linear accelerator system with a first multi-amplitude X-ray pulse and a second multi-amplitude X-ray pulse, an associated linear accelerator system and an associated computer program product with improved regulation.

The object is solved by the features of the independent claims. Advantageous configurations are described in the dependent claims.

• - Modulieren eines mittels einer Elektronenquelle des Linearbeschleunigersystems erzeugten ersten Elektronenstrahls innerhalb einer ersten Hochfrequenzpulsdauer in Abhängigkeit eines vorgegebenen Mehrfachamplituden-Röntgenstrahlenpuls-Profils, wobei der erste Mehrfachamplituden-Röntgenstrahlenpuls beim Modulieren des ersten Elektronenstrahls erzeugt wird,
• - Messen von zeitaufgelösten Ist-Werten des ersten Mehrfachamplituden-Röntgenstrahlenpuls mittels einer Messeinheit,
• - Anpassen zumindest eines Pulsparameters mittels einer Regeleinheit in Abhängigkeit eines Vergleichs des vorgegebenen Mehrfachamplituden-Röntgenstrahlenpuls-Profils und der gemessenen zeitaufgelösten Ist-Werte, und
• - Modulieren eines mittels der Elektronenquelle erzeugten zweiten Elektronenstrahls innerhalb einer zweiten Hochfrequenzpulsdauer in Abhängigkeit des zumindest einen angepassten Pulsparameters zur Erzeugung des zweiten Mehrfachamplituden-Röntgenstrahlenpuls, wodurch die Röntgenstrahlenpulskette geregelt wird.

The method according to the invention for controlling an X-ray pulse chain generated by means of a linear accelerator system with a first multi-amplitude X-ray pulse and a second multi-amplitude X-ray pulse has the following steps:

• - modulating a first electron beam generated by an electron source of the linear accelerator system within a first high-frequency pulse duration as a function of a predetermined multi-amplitude x-ray pulse profile, the first multi-amplitude x-ray pulse being generated when the first electron beam is modulated,
• - measuring time-resolved actual values of the first multi-amplitude X-ray pulse by means of a measuring unit,
• - Adaptation of at least one pulse parameter by means of a control unit depending on a comparison of the specified multiple-amplitude X-ray pulse profile and the measured time-resolved actual values, and
• - Modulating a second electron beam generated by means of the electron source within a second high-frequency pulse duration as a function of the at least one adjusted pulse parameter for generating the second multi-amplitude X-ray pulse, whereby the X-ray pulse chain is regulated.

In principle, it is conceivable that different categories of actual values are measured, for example a high-frequency power value, an amperage value, a dose value and/or an energy value. Measuring the time-resolved actual values advantageously enables the actual values of the first multi-amplitude x-ray pulse to be resolved over time. The time-resolved actual values are particularly advantageous because a single actual value, which describes the entire multi-amplitude X-ray pulse, has conventionally been recorded, in particular when a dose value of the multi-amplitude X-ray pulse is conventionally integrated over time. The measuring unit is in particular an impedance-matched measuring unit. In particular, the measuring unit can be terminated with 50 ohms. The time resolution is advantageously less than 1 μs, in particular less than 10 ns.

• - die Regeleinheit,
• - die Elektronenquelle,
• - die Hochfrequenzquelle,
• - die Messeinheit und
• - ein Target zur Generierung der Röntgenstrahlenpulskette auf. Vorteilhafterweise ermöglicht das Linearbeschleunigersystem ein geregeltes Generieren der Röntgenstrahlenpulskette, wodurch vorteilhafterweise die Materialdiskriminierung weiter verbessert wird.

The linear accelerator system according to the invention has

• - the control unit,
• - the electron source,
• - the high-frequency source,
• - the unit of measurement and
• - A target for generating the X-ray pulse chain. The linear accelerator system advantageously enables the X-ray pulse chain to be generated in a controlled manner, which advantageously further improves the material discrimination.

The x-ray pulse train includes the first multi-amplitude x-ray pulse and the second multi-amplitude x-ray pulse. Advantageously, the x-ray pulse chain comprises further regulated multi-amplitude x-ray pulses in addition to the first multi-amplitude x-ray pulse and the second multi-amplitude x-ray pulse, so that the x-ray pulse chain is continuously regulated during operation. This is made possible in particular if the time-resolved actual values are measured over the entire duration of an examination, for example in an image-based security check or in an image-based customs check.

The linear accelerator system is thus advantageously suitable for image-supported security checks or for image-supported customs checks, in particular when the regulated x-ray pulse chain is used to x-ray a transport item that is to be checked, typically with different materials, and is detected by a detector.

Conventionally, a distinction is made between two types of electron gun generation, continuous electron gun generation and pulsed electron gun generation. In the case of pulsed electron beam generation, a chain of X-ray pulses is typically generated by means of the linear accelerator system, which are generated due to the interaction of the electrons impacting a target of the linear accelerator system with a time offset, i.e. pulsed. The X-ray pulse chain generated according to the present invention can thus be assigned to pulsed electron beam generation.

The electron source typically emits the electrons into a linear accelerator cavity of the linear accelerator system. For example, the emitted electrons are represented by a time-resolved current value. The emitted electrons typically form at least two electron beams and are usually emitted over a period of time. The emitted electrons can be divided, for example, into a first electron beam and a second electron beam emitted at a later time than the first electron beam. A pulse duration of the first multi-amplitude x-ray pulse is substantially correlated in time with the pulse duration of the respective electron beams.

The electron source can have a thermionic emitter, for example a helical emitter or a spherical emitter, or a cold emitter, for example with carbon tubes or silicon. The electron beam with the current value is provided by the electron source and/or adjusted by means of the control unit. In addition, the electron source can have a blocking filter in the electron beam path for regulating the first electron beam and/or the second electron beam, for example in order to reduce a number of the electrons that have already been emitted. In particular, the control unit can control the emitter and/or the blocking grid, for example by setting a heating current and/or a blocking voltage. A variation of the current value includes, in particular, controlling the current amplitude, a pulse start and/or a pulse duration of the electron beam by means of the emitter and/or the blocking grid. For example, a capacitor can be charged to a level of a reverse grid voltage. In this case, the barrier grid can be regulated by switching the capacitor on or off. In this way, for example, the current intensity can be varied in a quasi-continuous manner, in particular if a number of capacitors are designed for this purpose. The capacitor can be switched on or off by means of a semiconductor switch, in particular a MOSFET and/or an IGPT and/or a transistor, for example in the nanosecond range.

The linear accelerator cavity can have several cells. A cell of the linac cavity is typically called an accelerator element. The linear accelerator cavity is in particular a resonator, for example a standing wave accelerator or a traveling wave accelerator.

The high-frequency source is designed to accelerate the electrons within the linear accelerator cavity and typically has a magnetron or a klystron. The high-frequency source can additionally have a reflection phase shifter device for quickly varying the high-frequency power value. The high-frequency power with the high-frequency power value is typically provided by the high-frequency source of the linear accelerator system and/or adjusted by means of the control unit of the linear accelerator system.

The magnetron is regularly used for a security check or customs control. The magnetron is a high-frequency oscillator that converts a high-voltage electrical pulse into a high-frequency pulse. In particular, the high voltage value correlates with the high frequency power value. A time course of the high-frequency power value is influenced, for example, by a high-voltage value increase and/or a high-voltage value decrease, for example as a result of a variation in the rate of change of the high-voltage value. In an alternative use of a klystron, in addition to the above variation, an amplitude of a high-frequency excitation field of the buncher cells can be varied. Another possibility is to modulate the high-frequency power by varying the high-frequency pulse.

In particular when the high-frequency source has the magnetron, the high-frequency source can additionally have a Marx generator for feeding the magnetron with the high voltage. The Marx generator typically has several stages. In this embodiment, the high-frequency power value is varied by switching on at least one stage of a Marx generator of the high-frequency source with a time delay, initiated by means of the control unit. In particular, the high-voltage value correlates with a number of switched-on stages of the Marx generator. According to this embodiment, at least one first high-frequency power value is thus achieved by the Marx generator, which is further increased by switching on the at least one stage with a time delay. The Marx generator therefore advantageously allows the high-frequency power to be adjusted by regulating the switched-on high-voltage value.

The delayed connection initiated by the control unit is particularly advantageous if a capacitance element, for example a connecting cable, is connected in parallel with the magnetron. In this case, according to the DE 10 2011 086 551 A1 conventionally, the high voltage value increase is chosen such that when the magnetron ignition voltage is reached, a charging current of the capacitance element is equal in amount to a working current of the magnetron, so that an impedance of the connecting cable is matched to an impedance of the magnetron. As a result, a rectangular magnetron pulse and thus a rectangular high-frequency pulse is conventionally achieved.

However, according to this embodiment of the present invention, the procedure is as follows: the impedance of the capacitance element, which is connected in parallel to the magnetron of the high-frequency source, is set at a ratio unequal to 1 to the impedance of the magnetron when the magnetron ignition voltage is reached, so that a high voltage value of the magnetron increases or falls depending on the time-delayed connection of the at least one stage. The capacitance element, the connection cable, in particular which is a coaxial cable. This embodiment is particularly advantageous because it means that the usual impedance matching of the elements of the high-frequency source can be dispensed with and/or the (mis)ratio of the impedances is advantageously used for setting the high-voltage value. The impedance ratio is essentially determined by the capacitive charging current and the working current of the magnetron. The impedance ratio can be influenced in particular by a change in the rise in the high-voltage value and/or by a variation in the point in time at which the at least one stage is switched on with a time delay.

The control unit is set up in particular to modulate the first electron beam and/or the second electron beam. The modulated first electron beam and/or the modulated second electron beam results in particular from the temporal variation of the high-frequency power value and/or the current strength value and/or the dose value and/or the energy value. In other words, the first electron beam and/or the second electron beam is modulated by varying the high-frequency power value and/or the current strength value and/or the dose value and/or the energy value. In the case of the variation over time, in particular the amplitude amount and/or a point in time for providing the amplitude amount is varied.

Basically, as part of a multi-amplitude X-ray pulse, several amplitude amounts of the energy values and/or the dose values are provided within a radio-frequency pulse duration. The multi-amplitude X-ray pulse may be, for example, as shown in lines E(t) and/or D(t) of FIG 4 until 6 be shown formed.

When a time interval is zero between two non-zero values, the multi-amplitude x-ray pulse comprises so-called intrapulses. The intrapulses are typically separated by the time slice equal to zero. The X-ray radiation is typically generated during the intrapulses. It follows that a multi-amplitude X-ray pulse can have a time segment during which no X-rays are generated for a short time, because no electrons are accelerated and therefore no X-rays can be generated, particularly when the high-frequency power is switched off and/or when the electron source is switched off.

It is thus defined that the x-ray pulse duration is equal to the radio frequency pulse duration. The x-ray pulse duration therefore specifies a period of time in which, in principle, a plurality of amplitude amounts occur and x-ray radiation can be generated as a function of those amplitude amounts not equal to zero. The X-ray pulse duration can be longer than the pulse duration of the electron beam, which in particular varies over time. If the multi-amplitude x-ray pulse has separated intra-pulses, the x-ray pulse duration comprises the time segment between the two intra-pulses during which no x-ray radiation is generated for a short time. In other words, the sum of the intra-pulse durations is shorter than the X-ray pulse duration in this case.

The modulation takes place in particular within the first radio-frequency pulse duration and/or the second radio-frequency pulse duration. The modulation includes in particular a temporal variation of the high-frequency power value of the high-frequency source and/or the current value of the electron beam. For example, the high-frequency power value and/or the current strength value and/or the energy value and/or dose value is varied within the first high-frequency pulse duration and the first electron beam is thus modulated. The second electron beam is modulated, for example, by varying the high-frequency power value and/or the current intensity value and/or the energy value and/or dose value within the second high-frequency pulse duration. Due to the variation of the high-frequency power value and/or the current strength value, the energy value and/or the dose value can be varied due to their dependency.

The first high-frequency pulse duration and/or the second high-frequency pulse duration usually includes a respective time period in which the high-frequency source provides a high-frequency power, in particular not equal to zero, for accelerating the electrons within the linear accelerator cavity. The first high-frequency pulse duration and the second high-frequency pulse duration can differ in terms of a time extension, but are typically of the same length. The first radio frequency pulse and the second radio frequency pulse are typically interrupted by a period of time in which the radio frequency source is not providing radio frequency power to accelerate the electrons within the linear accelerator cavity. It follows that between the first multi-amplitude x-ray pulse and the second multi-amplitude x-ray pulse, the radio frequency power is typically zero. In the same period of time, the current value is usually also zero. In addition, the current strength value can be zero during the first radio-frequency pulse duration and/or the second radio-frequency pulse duration, in order to separate the two intra-pulses, for example.

The multi-amplitude x-ray pulse profile is usually a time-resolved profile. The multiple amplitude X-ray pulse profile is specified by the control unit, for example, and can be and/or can be set by the control unit depending on at least one specified high-frequency power value, current intensity value, dose value and/or energy value. This dependency can be represented in the form of a pulse parameter. The at least one pulse parameter brings about a variation over time in the high-frequency power value and/or the current intensity value and/or the energy value and/or the dose value. The control unit can apply the pulse parameter and thus cause typically the high-frequency power value and/or the current value and/or the energy value and/or the dose value to be varied. The multiple amplitude X-ray pulse profile specifies in particular the time course of the X-ray pulse to be generated during operation with the specified high-frequency power value, current strength value, dose value and/or energy value.

The high-frequency power value, the current strength value, the dose value and/or the energy value depend in particular on one another and/or are mutually dependent. The high-frequency power value P(t) is usually given in W, the current value I(t) in A, the energy value E(t) in eV and the dose value D(t) in Gy. For example, the energy value is calculated from the third root of a fraction with the dose value in the numerator and the current value in the denominator: $$E\propto \sqrt[3]{\frac{D}{I}}$$

From this it follows in turn: $$D\propto I\cdot {\mathrm{<figure-callout\; id="3"\; label="E"\; filenames="DE102020214128B4\_0005.png,DE102020214128B4\_0009.png"\; state="\{\{state\}\}">E</figure-callout>}}^3$$

The dose value is proportional to the high-voltage amplitude U(t) with the unit V to the power of 3. The high-voltage amplitude U(t) in turn influences the high-frequency power value P(t).

One embodiment provides that the time-resolved actual values describe a dose distribution of the first multi-amplitude X-ray pulse. In particular, the dose value distribution represents the course of the dose over time, with the course of the dose having a plurality of dose values. The dose value distribution is typically not constant within the first multi-amplitude X-ray pulse duration. In other words, the dose values usually vary within the respective high-frequency pulse duration.

An advantageous development of the previous embodiment is in particular that the measuring unit for measuring the dose value distribution is an ionization chamber, a photo scintillator or a directly converting semiconductor.

One embodiment provides that the time-resolved actual values describe an energy value distribution of the first multi-amplitude X-ray pulse. The energy value distribution represents, in particular, the course of energy over time, with the course of energy having a number of energy values. The energy value distribution is typically not constant within the first multi-amplitude x-ray pulse duration. In other words, the energy values vary within the respective high-frequency pulse duration.

An advantageous development of the previous embodiment is in particular that the measuring unit for measuring the energy value distribution is a current measuring device connected to a target of the linear accelerator system or a measuring transformer surrounding the electron beam path of the X-ray pulse chain.

In a particularly advantageous embodiment of the invention, the time-resolved actual values describe the dose value distribution and the energy value distribution. This embodiment is particularly advantageous because it allows both variables to be controlled. In particular, the control unit is designed for this purpose, which advantageously compares the measured actual energy values and the measured actual dose values in a control loop with the specified multiple-amplitude X-ray pulse profile and accordingly adjusts the at least one pulse parameter, so that the subsequent multiple-energy X-ray pulse according to the at least one pulse parameter adjusted and regulated. This embodiment is particularly advantageous when the actual values of the first multi-amplitude X-ray pulse are measured with a time resolution of less than 1 μs. The time resolution is particularly advantageously less than 10 ns.

An embodiment provides that the multi-amplitude X-ray pulse profile has a continuous and variable amplitude profile for an energy value distribution with increasing and/or decreasing energy values. The constant amplitude profile is in particular stepless and/or continuous, for example linearly increasing or decreasing, in particular between a first amplitude value greater than zero and a second amplitude value greater than zero. Such a multi-amplitude X-ray pulse profile is advantageously made possible by the fact that the time resolution is less than 1 μs and the time-resolved ten actual values describe the dose value distribution and the energy value distribution.

An alternative embodiment to the previous embodiment provides that the multi-amplitude x-ray pulse profile has at least two separate intra-pulses. This multiple amplitude X-ray pulse profile is advantageously made possible by the fact that the time resolution is less than 1 μs and the time-resolved actual values describe the dose value distribution and the energy value distribution. Another advantage is that the two separate intrapulses can be controlled separately from each other. Between the two separate intrapulses, the current intensity value is typically equal to zero.

The computer program product can be a computer program or can comprise a computer program. The computer program product has, in particular, the program code means that map the method steps according to the invention. As a result, the method according to the invention can be defined and executed in a repeatable manner, and control over the transfer of the method according to the invention can be exercised. The computer program product is preferably configured in such a way that the computing unit can carry out the method steps according to the invention using the computer program product. In particular, the program code means can be loaded into a memory of the processing unit and typically executed by means of a processor of the processing unit with access to the memory. If the computer program product, in particular the program code means, is executed in the computing unit, typically all embodiments according to the invention of the method described can be carried out. The computer program product is stored, for example, on a physical, computer-readable medium and/or stored digitally as a data package in a computer network. The computer program product can represent the physical, computer-readable medium and/or the data package on the computer network. The invention can also start from the physical, computer-readable medium and/or the data packet in the computer network. The physical, computer-readable medium can usually be connected directly to the processing unit, for example by inserting the physical, computer-readable medium into a DVD drive or plugging it into a USB port, which means that the processing unit can read the physical, computer-readable medium in particular. The data packet can preferably be retrieved from the computer network. The computer network can have the processing unit or be indirectly connected to the processing unit by means of a wide area network (WAN) or a (wireless) local area network connection (WLAN or LAN). For example, the computer program product can be stored digitally on a cloud server at a storage location of the computer network, by means of the WAN via the Internet and/or by means of the WLAN or LAN to the processing unit, in particular by calling up a download link that refers to the storage location of the computer program product , be transmitted.

Features, advantages or alternative embodiments mentioned in the description of the device are also to be transferred to the method and vice versa. In other words, claims to the method can be further developed with features of the device and vice versa. In particular, the device according to the invention can be used in the method.

The invention is described and explained in more detail below with reference to the exemplary embodiments illustrated in the figures. Basically, in the following description of the figures, structures and units that remain essentially the same are named with the same reference symbols as when the respective structure or unit first appeared.

• 1 ein Verfahren für ein Regeln einer mittels eines Linearbeschleunigersystems generierten Röntgenstrahlenpulskette mit einem ersten Mehrfachamplituden-Röntgenstrahlenpuls und einem zweiten Mehrfachamplituden-Röntgenstrahlenpuls in einem ersten Ausführungsbeispiel,
• 2 das Verfahren von 1 in einem zweiten Ausführungsführungsbeispiel,
• 3 eine in der Regeleinheit implementierte Regelschleife,
• 4 beispielhafte Verläufe des Hochfrequenzleistungswerts P(t), des Dosiswerts D(t) und des Energiewerts E(t) in Abhängigkeit von der zeitlichen Variation des Stromstärkewerts I (t) ,
• 5 beispielhafte Verläufe des Stromstärkewerts I(t), des Dosiswerts D(t) und des Energiewerts E(t) in Abhängigkeit von der zeitlichen Variation des Hochfrequenzleistungswerts P(t),
• 6 beispielhafte Verläufe des Dosiswerts D(t) und des Energiewerts E(t) in Abhängigkeit von der zeitlichen Variation des Hochfrequenzleistungswerts P(t) und des Stromstärkewerts I(t),
• 7 den Verlauf des Hochfrequenzleistungswerts P(t) in Abhängigkeit von einer Hochspannungsamplituden U(t),
• 8 ein Linearbeschleunigersystem mit einer Vorhersage-Regelschleife und
• 9 ein Linearbeschleunigersystem mit einer direkten Regelschleife.

Show it:

• 1 a method for controlling an X-ray pulse chain generated by means of a linear accelerator system with a first multi-amplitude X-ray pulse and a second multi-amplitude X-ray pulse in a first exemplary embodiment,
• 2 the procedure of 1 in a second embodiment,
• 3 a control loop implemented in the control unit,
• 4 exemplary curves of the high-frequency power value P(t), the dose value D(t) and the energy value E(t) as a function of the time variation of the current value I (t) ,
• 5 example curves of the current value I(t), the dose value D(t) and the energy value E(t) as a function of the temporal variation of the high-frequency power value P(t),
• 6 example curves of the dose value D(t) and the energy value E(t) as a function of the temporal variation of the high-frequency power value P(t) and the current value I(t),
• 7 the course of the high-frequency power value P(t) as a function of a high-voltage amplitude U(t),
• 8th a linear accelerator system with a predictive control loop and
• 9 a linear accelerator system with a direct control loop.

1 shows a flowchart of a method for controlling an x-ray pulse chain generated by means of a linear accelerator system with a first multi-amplitude x-ray pulse and a second multi-amplitude x-ray pulse.

Method step S100 characterizes modulation of a first electron beam generated by an electron source of the linear accelerator system within a first high-frequency pulse duration as a function of a predetermined multi-amplitude X-ray pulse profile, the first multi-amplitude X-ray pulse being generated when the first electron beam is modulated. In particular, the multi-amplitude X-ray pulse profile can have a steady and variable amplitude profile for an energy value distribution with increasing and/or decreasing energy values. Alternatively, the multi-amplitude x-ray pulse profile may include at least two separate intra-pulses.

Method step S101 indicates a measurement of time-resolved actual values of the first multi-amplitude X-ray pulse by means of a measuring unit. In particular, the time-resolved actual values describe a dose value distribution of the first multi-amplitude X-ray pulse, the measuring unit for measuring the dose value distribution being an ionization chamber, a photo scintillator or a directly converting semiconductor. Alternatively or additionally, the time-resolved actual values describe an energy value distribution of the first multi-amplitude X-ray pulse, the measuring unit for measuring the energy value distribution being a current measuring device connected to a target of the linear accelerator system or a measuring transformer surrounding the electron beam path of the X-ray pulse chain. The actual values of the first multi-amplitude X-ray pulse are preferably measured with a time resolution of less than 1 μs, particularly advantageously the time resolution is less than 10 ns.

Method step S102 characterizes an adjustment of at least one pulse parameter by means of a control unit as a function of a comparison of the specified multiple-amplitude x-ray pulse profile and the measured time-resolved actual values.

Method step S103 characterizes a modulation of a second electron beam generated by the electron source within a second high-frequency pulse duration depending on the at least one adjusted pulse parameter for generating the second multi-amplitude X-ray pulse, whereby the X-ray pulse chain is regulated.

2 shows further method steps in addition to the method steps S100 to S103.

Method step S104 indicates that the high-frequency power value is varied by switching on at least one stage of a Marx generator of the high-frequency source with a time delay, initiated by means of the control unit, and that an impedance of a capacitance element, which is connected in parallel to a magnetron of the high-frequency source, is proportional when the magnetron ignition voltage is reached is set equal to 1 to the impedance of the magnetron, so that a high voltage value of the magnetron increases or decreases depending on the time-delayed connection of the at least one stage.

3 shows a control loop implemented in the control unit 11 . The multiple amplitude X-ray pulse profile is set as a function of at least one predefined dose value D_soll and energy value E_soll by a control algorithm unit 11.R1 of the control unit 11 determining the corresponding high-frequency power value P_soll and the corresponding current intensity value Isoll. The determined values P_soll, I_soll can be mapped in at least one pulse parameter in such a way that a multi-amplitude X-ray pulse P1, P2 is generated in the linear accelerator system 10 by modulating the electron beam. An alternative designation of the determined values P_soll, I_soll can be P_stell, I_stell. The time-resolved actual values D_actual, E_actual are measured using the measuring unit 12 and could therefore alternatively be referred to as D mess or E mess

Basically it is conceivable that the control unit 11 is equipped with two control sub-units such that the first control sub-unit controls a first intra-pulse of the multi-amplitude X-ray pulse and the second control sub-unit controls a second intra-pulse of the multi-amplitude X-ray pulse.

4 shows exemplary curves of the high-frequency power value P(t), the dose value D(t) and the energy value E(t) as a function of the temporal variation of the current intensity value I(t) in variants #1 to #4. The dash-dot circles illustrate the variation of the current strength values I(t) as a controlled variable. The dashed alternative course at The energy values E(t) shows a fictitious course of the energy values without load, in particular with a continuous current value I(t) equal to zero.

5 shows exemplary curves of the current strength value I(t), the dose value D(t) and the energy value E(t) as a function of the time variation of the high-frequency power value P(t) in variants #5 to #7. The dash-dot circles illustrate the variation of the high-frequency power values as a controlled variable. The dashed, alternative course for the energy values E(t) shows a fictitious course of the energy values without load, in particular with a continuous current strength value I(t) equal to zero.

6 shows exemplary curves of the dose value D(t) and the energy value E(t) as a function of the temporal variation of the high-frequency power value P(t) and the current value I(t) in variant #8. In this embodiment, the linearly increasing course, which is an example of a constant and variable amplitude profile, of the energy value E(t) during the entire radio-frequency pulse duration should be emphasized in particular. The dashed, alternative course for the energy value E(t) shows a fictitious course of the energy values without load, in particular with a continuous current strength value I(t) equal to zero. For this embodiment, for example, the 3 control loop shown can be used.

7 shows the course of the high-frequency power value P(t) as a function of a high-voltage amplitude U(t) in rows #9 to #12. The high-voltage amplitude increase is defined in particular as the rate of change of the high-voltage amplitude U(t).

In particular, rows #9 to #11 show that the course of the high-frequency power value P(t) is directly related to the high-voltage amplitude increase. In particular, the relationship is such that a sharp rise in high-voltage amplitude can lead to a falling high-frequency power value P(t) and a slow rise in high-voltage amplitude can lead to a rising high-frequency power value P(t).

Row #12 discloses in particular that the high-frequency power value P(t) can be increased by the high-voltage amplitude U(t) being suddenly increased, in particular due to the time-delayed connection of at least one stage of a Marx generator of the high-frequency source.

8th Figure 1 shows a prior art linear accelerator system 10 with a predictive control loop.

9 shows the linear accelerator system 10 with several control loops according to the invention and various options 1 to 5 for controlling the linear accelerator system 10.

• - eine Regeleinheit 11,
• - eine Elektronenquelle 13,
• - eine Hochfrequenzquelle 14,
• - eine Messeinheit 12 und
• - ein Target zur Generierung der Röntgenstrahlenpulskette auf.

The linear accelerator system 10 has

• - a control unit 11,
• - an electron source 13,
• - a high-frequency source 14,
• - a measuring unit 12 and
• - A target for generating the X-ray pulse chain.

Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is nevertheless not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims (13)

Method for controlling an X-ray pulse chain generated by means of a linear accelerator system with a first multi-amplitude X-ray pulse and a second multi-amplitude X-ray pulse, having the following steps: - modulating a first electron beam generated by an electron source of the linear accelerator system within a first high-frequency pulse duration as a function of a predetermined multi-amplitude x-ray pulse profile, the first multi-amplitude x-ray pulse being generated when the first electron beam is modulated, - measuring time-resolved actual values of the first multi-amplitude X-ray pulse by means of a measuring unit, - Adaptation of at least one pulse parameter by means of a control unit depending on a comparison of the specified multiple-amplitude X-ray pulse profile and the measured time-resolved actual values, and - Modulating a second electron beam generated by means of the electron source within a second high-frequency pulse duration as a function of the at least one adjusted pulse parameter for generating the second multi-amplitude X-ray pulse, whereby the X-ray pulse chain is regulated. procedure after claim 1 , wherein the time-resolved actual values describe a dose value distribution of the first multi-amplitude X-ray pulse. procedure after claim 2 , wherein the measuring unit for measuring the dose value distribution is an ionization chamber, a photo scintillator or a directly converting semiconductor. Method according to one of the preceding claims, wherein the time-resolved actual values describe an energy value distribution of the first multi-amplitude X-ray pulse. procedure after claim 4 , wherein the measuring unit for measuring the energy value distribution is a current measuring device connected to a target of the linear accelerator system or a measuring transformer surrounding the electron beam path of the X-ray pulse chain. Method according to one of the preceding claims, in which the high-frequency power value is varied by switching on at least one stage of a Marx generator of the high-frequency source with a time delay initiated by means of the control unit. procedure after claim 6 , wherein an impedance of a capacitance element, which is connected in parallel to a magnetron of the high-frequency source, is set at a ratio unequal to 1 to the impedance of the magnetron when the magnetron ignition voltage is reached, so that a high-voltage value of the magnetron increases or decreases depending on the time-delayed connection of the at least one Step. A method according to any one of the preceding claims, wherein the actual values of the first multi-amplitude X-ray pulse are measured with a time resolution of less than 1 µs. procedure after claim 8 , where the time resolution is less than 10 ns. A method according to any one of the preceding claims, wherein the multi-amplitude X-ray pulse profile comprises a steady and variable amplitude profile for an energy value distribution with increasing and/or decreasing energy values. Procedure according to one of Claims 1 until 9 , wherein the multi-amplitude X-ray pulse profile comprises at least two separate intrapulses. Linear accelerator system comprising - a control unit for carrying out a method according to one of the preceding claims, - an electron source, - a high-frequency source, - a unit of measurement and - a target for generating the X-ray pulse chain. Computer program product, which can be loaded directly into a memory of a computing unit, with program code means to implement a method according to one of Claims 1 until 11 to be carried out when the computer program product is executed in the processing unit.

Images